Continuous process for the electrogalvanizing of metal strip in a chloride-based plating solution in order to obtain coatings with low rugosity at high current densities

Abstract

An electrogalvanizing process, in which a strip is moved past an anode, plating solution is made to flow at a speed V with respect to the moving strip, and an electric current of current density J greater than 50 A/dm 2 is passed between the strip and the anode, which comprises carrying out the deposition under conditions such that: J/J lim is less than or equal to 0.15; J 2 /J lim is less than or equal to 22 A/dm 2 ; where J lim is the limiting current density, corresponding to the current density plateau in the current versus potential curve characteristic of the plating solution flowing at the speed V in the vicinity of the strip. An electroplating cell of the radial type for implementing the process, in which cell the anode bed is continuous, is disclosed. The process facilitates the high-speed deposition of zinc which has low rugosity and is free of edge dendrites.

What is claimed is: 
     
       1. A continuous process for the electrogalvanizing of a metal strip in a chloride-based plating solution, in which said strip is moved past an anode, said solution is made to flow at a speed V through the gap separating said strip from said anode, the speed V being measured with respect to said moving strip, an electric current corresponding to a current density J greater than 50 A/dm 2  is passed between said strip forming the cathode and said anode, which comprises carrying out the deposition under conditions such that: J/J lim  is less than or equal to 0.15, and   J 2  /J lim  is less than or equal to 22 A/dm 2  to prevent the formation of edge dendrites on the resulting galvanized metal strip,   where J lim  is the limiting current density corresponding to the current-density plateau in the current v potential curve characteristic of said plating solution flowing at the speed V in the vicinity of the strip.   
     
     
       2. The continuous process defined in claim 1, wherein J/J lim  is less than or equal to 0.15 to limit the rugosity added to the resulting galvanized metal strip to about 0.25 microns or less.